The invention relates to devices for transferring small amounts of liquid from a liquid holder to a liquid destination, e.g., a thin layer chromatography plate.
Thin layer chromatography is a technique for analyzing the components of a liquid sample. In thin layer chromatography, a flat plate is covered with an absorbent media, or a xe2x80x9cstationary phase.xe2x80x9d A drop of sample dissolved in a solvent, or a xe2x80x9cmobile phase,xe2x80x9d is applied to the flat plate. Due to capillary action, the solvent moves along the absorbent media on the plate. As the solvent moves, the components of the sample separate and deposit on the absorbent media at different points, depending on certain characteristics of the component, such as molecular weight and affinity for the absorbent media. Once the solvent has stopped traveling and has completed depositing the components of the sample, a technician can analyze the patterns and materials deposited on the plate to determine information about the composition of the sample.
To begin thin layer chromatographic analysis, a technician must transfer a drop of the sample-solvent mixture from a liquid holder, e.g., a test tube, to the flat plate. Typically, a laboratory technician transfers small amounts of liquid using a thin, rigid glass or plastic tube called a pipette. To transfer liquid with a pipette, an end of the pipette is placed in contact with liquid in the test tube. Since the diameter of the pipette is small, a drop of liquid is drawn into the tube by capillary action. The tube, with the drop inside, is then transferred to the flat plate. When the open end of the tube is touched against the absorbent media on the glass plate, capillary action pulls the drop of liquid from the pipette to the absorbent media.
Conventional pipettes, however, have certain limitations. Since pipettes are typically rigid and fragile, pressing a pipette against a flat surface with too much force can break the pipette. For this reason, technicians generally must transfer liquid from test tubes to a thin layer chromatography plate one pipette at a time, and one drop at a time.
In one aspect, the invention features a device for transferring small drops of liquid from one or more liquid holders to one or more liquid destinations. The device includes a support member and a plurality of fluid transfer members extending from the support member. Each fluid transfer member includes a flexible liquid transfer end.
Embodiments of this aspect of the invention may include one or more of the following features.
The fluid transfer members have a generally elongated shape, and extend from the support member axially in a parallel arrangement. Each transfer member is sized and shaped to fit within a test tube.
The device further includes an adjusting mechanism, e.g., a spring, that allows a user to vary the distance between two fluid transfer members. For example, the device can include separate adjusting mechanisms connecting each fluid transfer member to adjacent fluid transfer members, such that a user can simultaneously vary the distance between all the fluid transfer members.
The fluid transfer ends can include a sponge tip. For example, the fluid transfer end can be a rigid shaft that includes a sponge tip, the shaft being removably attached to a holder. The device can further include a plunger that, when activated, ejects one or more fluid transfer ends from its holder.
The sponge tips are made from urea formaldehyde, polyethylene, or cotton, and have diameters less than about 1.5 mm.
Instead of a sponge tip, each fluid transfer end can include a capillary tube at its distal tip and an axially extending spring. The spring is coupled to, e.g., a proximal end of the capillary tube such that the spring provides axial flexibility to the tube.
In the capillary tube embodiment, each fluid transfer member can include a rigid sleeve and a pin. The sleeve has a proximal region that surrounds the spring and a distal region that defines the capillary tube, and the pin has a shaft and a head. The shaft of the pin extends axially into the spring, and the head of the pin is coupled to a holder. Each holder defines a threaded bore and includes a pair of screws threadingly engaged with the bore. The head of the pin is disposed within the bore between the two screws. The capillary tube also defines a transverse hole to prevent air from becoming trapped within the tube.
In another aspect, the invention features a fluid transfer tool for use with the fluid transfer devices described herein. The tool includes an axially extending spring, a capillary tube coupled to a distal end of the spring, and a pin. The pin has a shaft disposed within the interior of spring, and a head that remains proximal to the proximal end of the spring. The tool also includes an attachment mechanism, such as a threaded screw, for coupling the tool to the fluid transfer device. The tool can be, e.g., a replacement fluid transfer end for the fluid transfer device, and can be sold separately from the device.
In another aspect, the invention features a method of transferring a drop of liquid from a liquid holder to a liquid destination (e.g., a thin layer chromatography plate or an electrophoresis gel). The method includes: (a) providing a fluid transfer device that has an elongated shaft with a flexible, liquid transfer end; (b) contacting the end with liquid in the liquid holder, such that the end collects a drop of liquid; and (c) contacting the end against the liquid destination, such that the tip releases the drop of liquid.
Embodiments of this aspect of the invention may include one or more of the following features.
The drop of liquid is less than about 0.005 ml in volume. The liquid transfer end includes a sponge tip, or is spring mounted, the spring providing the end with axial flexibility.
In another aspect, the invention features a method of simultaneously transferring a plurality of liquid drops from one or more liquid holders to one or more liquid destinations. The method includes: (a) providing a fluid transfer device that has a support member and a plurality of fluid transfer members extending from the support member, where each fluid transfer member includes a flexible, liquid transfer end; (b) contacting the liquid transfer end of more than one fluid transfer member with liquid in one or more liquid holders, such that each end contacted with liquid collects a drop of liquid; and (c) simultaneously contacting the liquid absorbing end of each more than one fluid transfer members against one or more liquid destinations, such that each end contacted with a liquid destination releases its collected drop to the liquid destination.
Embodiments of this aspect of the invention may include one or more of the following features. The fluid transfer members extend axially from the support member, and each liquid transfer end is axially flexible. For example, each fluid transfer end includes a capillary tube at its distal tip, and an axially extending spring, the spring being coupled to the capillary tube such that the spring provides the axial flexibility to the tube. The second contacting step includes pressing the distal tip of at least one fluid transfer end against a surface of the liquid destination, such that the spring of the at least one fluid transfer member is compressed. Alternatively, the liquid transfer ends can each include a sponge tip.
The first contacting step includes contacting each end in the device with liquid in a liquid holder, and the second contacting step includes contacting each end in the device against a liquid destination.
The liquid destination is, e.g., a thin layer chromatography plate, and the one or more liquid holders is an array of test tubes. The first contacting step includes simultaneously contacting different liquid absorbing tips with liquid in different test tubes.
Each fluid transfer member can have a disposable portion that includes its liquid transfer end. If the ends are disposable, the method further includes removing one or more disposable portions from the device after contacting one or more ends against a liquid destination.
Embodiments of the invention may include one or more of the following advantages. The flexible fluid transfer ends are less likely to break when pressed against, e.g., a thin layer chromatography plate. The flexibility of the ends allows the device to tolerate some variation in the lengths of the fluid transfer members.
The fluid transfer devices are safer to use than rigid pipettes, since the fluid transfer ends are less likely to break than pipettes, and therefore less likely to expose a user to chemicals.
Since the fluid transfer devices can transfer liquid from multiple liquid holders to multiple liquid destinations simultaneously, they are faster to use than individual pipettes.